AI solution for JavaScript Coding Question on BFE.dev
13. Implement a Queue by using Stack

One possible solution is to use two Stacks, one for storing the elements in the same order they are enqueued (inStack), and another for reversing the order of the elements for dequeuing (outStack). When outStack is empty, all elements of inStack are popped and pushed into outStack, reversing their order.

class Queue {
  constructor() {
    this.inStack = new Stack();
    this.outStack = new Stack();
  }
  enqueue(element) {
    this.inStack.push(element);
  }
  peek() {
    if (this.outStack.size() === 0) {
      this.transfer();
    }
    return this.outStack.peek();
  }
  dequeue() {
    if (this.outStack.size() === 0) {
      this.transfer();
    }
    return this.outStack.pop();
  }
  size() {
    return this.inStack.size() + this.outStack.size();
  }
  transfer() {
    while (this.inStack.size() > 0) {
      this.outStack.push(this.inStack.pop());
    }
  }
}

In this implementation, enqueue() simply adds the element to the inStack (which represents the tail of the queue), while peek() and dequeue() first transfer all the elements from inStack to outStack (if necessary), ensuring that outStack represents the head of the queue, and then they return or remove the top element, respectively. size() returns the sum of the sizes of both stacks. The transfer() method pops all elements from inStack and pushes them into outStack, reversing their order. This method is only called when outStack is empty, which means that the next peek or dequeue operation must reverse the order of the elements.